Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $227.91   13.571%   $258.8397   $258.84   $258.85   $258.80  
  Purchase #2 $232.61   11.719%   $259.8696   $259.87   $259.85   $259.90  
  Purchase #3 $50.59   12.270%   $56.7974   $56.80   $56.80   $56.80  
  Purchase #4 $164.91   5.469%   $173.9289   $173.93   $173.95   $173.90  
  Purchase #5 $41.53   13.719%   $47.2275   $47.23   $47.25   $47.20  
  Purchase #6 $238.35   13.661%   $270.911   $270.91   $270.90   $270.90  
  Purchase #7 $148.99   11.749%   $166.4948   $166.49   $166.50   $166.50  
  7 purchase totals = $1,104.89       $1,234.0689   $1,234.07   $1,234.10   $1,234.00